The invention concerns a column unit, in particular a chair column unit, comprising a base tube with a base-tube axis, with a first base-tube end, and with guides inserted in the base tube in the area of the second base-tube end; furthermore comprising a positioning device, with a device axis which substantially coincides with the base-tube axis; with a first component-group unit and a second component-group unit, with these component-group units being movable axially to each other and lockable in a plurality of axial relative positions against each other; with furthermore the first component-group unit being supported, on a support connected to the base-tube, in a manner that is substantially immovable axially with respect to the base tube and which is, if applicable, rotatable with respect to the support; with furthermore the second component-group unit extending beyond the second base-tube end and being adjustable between an innermost position and an outermost position with respect to the second base-tube end; with furthermore an outer section of the second component-group unit, extending beyond the second base-tube end and beyond the guides, being shaped to connect with a column-borne object; and with the second component-group unit being in axially sliding engagement with the guides.
Such a column unit is known, for instance, from German Patent Document 19 31 012 and from U.S. Pat. No. 4,848,524. In the case of the known forms of embodiment, which have been eminently successful in practice, the guides are arranged in an axially attached manner with respect to the second (i.e., upper) base-tube end. This may cause the problem that the upper (i.e., second) component-group unit no longer has a sufficient guide length at the guides when the second component-group unit is in its outermost position. Moreover, this problem cannot be solved simply by increasing the length of the base tube while leaving the positioning device unchanged because such a lengthening of the base tube could possibly lead to a restriction in the travel of the positioning device, so that the shortest-possible position as designed for the column unit could no longer be achieved.